hv_netvsc: Fix the queue index computation in forwarding case

If the outgoing skb has a RX queue mapping available, we use the queue
number directly, other than put it through Send Indirection Table.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>